In 1975, a report was presented at the 19th Stapp Car Crash Conference by personnel from the Technical University of Berlin describing the possibility of concentrated lower rib cage loading from a belt restraint system. A second report presented at the 1977 Stapp Conference expanded on the subject. No evidence was available, however, that such concentrated loading was occurring in most highway accidents, although rib fracture was known to occur in severe highway crashes, particularly with older occupants.
During developmental tests conducted by personnel of the assignee of the present application on one proposal for an experimental passive restraint system early in 1979, strain gages were applied to several dummy ribs to permit a comparison of the strain distribution on the dummy chest when restrained by the experimental system and by a production belt system. Significant differences were noted in this test program in the dummy rib strain gage measurements. Although the strain gaged ribs did demonstrate that differences were present, they could not provide actual load data to measure the magnitude of loading on different parts of the rib cage for the following reasons.
1. The dummy rib cage used was a poor representation of the skeletal shape of the human rib cage.
2. Once a rib was stressed beyond its yield point, the data could not be quantified and the rib transducer was ruined.
3. Without elaborate instrumentation techniques, different chest loading patterns tended to distort or even cancel out the strain measurements of interest. Thus, the reliability of such measurements tended to be low.
4. Because of the possible complicated load patterns on the ribs, it became apparent it would be very difficult to ever obtain a vectored load reading in pounds at an angle of application.
To better understand these complicated load patterns, a transducer is required that is capable of accurately measuring the gross load distribution and direction of loading over a dummy rib cage during a restraint system test. By using such a transducer, it is possible to quantify the effect of restraint system variables on chest loading patterns.
Design constraints for the proposed transducer comprise a rib cage simulation that:
1. Has the approximate size and shape of a partly compressed human rib cage;
2. Completely isolates the forces into the lower rib cage from those applied to the rest of the chest;
3. Provides triaxial load measurement in at least four key locations on the rib cage;
4. Provides sufficient chest deflection properties to stabilize the belt location on the chest;
5. Utilizes the head, neck, arms and lower torso of currently available or future dummies;
6. Has essentially the same weight and weight distribution of a nontransducer dummy chest;
7. Accommodates for frontal (+30.degree.) impacts only; and
8. Is durable, reliable and easy to use.